This invention relates to apparatus for mixing and dispensing a plurality of liquids and more especially is directed to apparatus for mixing and dispensing the chemical reactants for forming polyurethane foam.
As is well known to those skilled in the art, the use of synthetic foams, especially of the polyurethane type, is growing for numerous users. Despite this, the users have been required to use dispensing equipment which is somewhat less than completely satisfactory. Much of this results from the fact that polyurethane "sets" in the dispenser -- within the mixing chamber or the nozzle (which may be one and the same), which, eventually makes the system inoperative. The freeze or set problem becomes more critical when the dispensing system is used intermittantly. In some present systems, an interruption in pouring or dispensing for even 30 seconds can result in solidification of material within the dispenser.
To overcome these problems the art has generally developed along three lines viz:
1. Throw away nozzles. The nozzle containing the mixing chamber is replaced practically everytime there is an interruption in pour. For large scale use the economics of this is not particularly desirable.
2. The so-called "Solvent Flush" systems. After every dispensing action a small volume usually in the order of a few ounces of cleaning solvent, is passed through the mixing chamber to clean it. This is messy, affords some cleaning action, but in actual practice it has been found necessary to disassemble such dispensers every day after use for a thorough cleaning.
3. Dispensers containing valving rods as disclosed in Gusmer U.S. Pat. Nos. 2,890,836 and 3,263,928. In these patents a tight fitting cylindrical valving rod movable in a cylindrical mixing chamber is used, and the rod attempts to scrape the mixing chamber clean as it moves. This works fairly well except here too in practice, is is necessary to disassemble the dispenser every day after use for a thorough cleaning.
In the dispensing apparatus which I have disclosed and claimed in my U.S. Pat. No. 3,687,370, many of the foregoing problems in polyurethane dispensing have been overcome, and such units operate for extended period without cleaning. In such apparatus the cylindrical valving rod at each retraction is withdrawn into a solvent which serves for cleaning purposes. Upon protraction of the rod, a small amount of such solvent is carried into the mixing chamber for cleaning purposes.
The present invention is an improvement over the dispensing apparatus of my above noted patent, in that I now provide for substantially better cleaning of the valving rod and mixing chamber, and at the same time improve the flow of liquid through the entry ports and the sealing capability of the valving rod. How this is accomplished is set forth as this description proceeds.
Essentially, in this invention I make use of a partially flattened valving rod, to provide a self cleaning polyurethane dispenser and the like. The mode of operation is essentially the same as set out in my prior patent, the teachings of which are incorporated by reference herein.